Like any computer, a Mac is prone to serious problems over the course of its life. A wide variety of things can go horribly, horribly wrong. From a complete failure to start to that terrifying kernel panic screen, here's how to troubleshoot (and hopefully fix) what's plaguing your Mac.

For the most part, the problems you run into on a Mac are pretty universal across all versions of OS X, but we'll stick to the most modern operating systems here: Lion and Mountain Lion (most of these tips should also work with Snow Leopard though). If you're still covered by Apple's warranty or AppleCare, the easiest solution is to walk into the Apple Store and have them fix everything for free. If you don't want to waste time or you're not covered anymore, you can do a lot of the troubleshooting yourself.

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The Problem: Blue or Grey Screen on Startup

When you turn on your computer and get a grey or blue screen (or it gets stuck at the Apple logo) that never loads OS X, it's a pretty good cause for concern. This can happen for a number of reasons, so it's one of the most frustrating things that can happen to a Mac, and troubleshooting it is no easy task. So, let's break it down into a few steps you can take to figure out what's going on.

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Step One: Disconnect All Peripherals

One of the main causes of a grey or blue screen on startup is incompatible hardware connected to the machine. This might be a printer, an external hard drive, or even a USB hub. So, disconnect everything except the mouse and keyboard, and restart your computer.

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If your Mac starts this way, then it's an issue with one of those peripherals. You have to trial-and-error your way through to figure out which one, so connect them back into your computer one by one, and restart. If one of them causes your computer to hang on the grey screen again, you've found your issue.

If you figure out the problematic peripheral, it's time to do a little research. Head to the manufacturer's web site and see if others are reporting the same problem. You might be able to fix it with a software update or a firmware update to the device.

If no devices are causing problems, and your Mac still won't boot, then it's time to dig a little deeper.

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Step Two: Perform a Safe Boot

Safe boot makes your Mac boot up with the minimum amount of drivers needed to make it work, and it checks your hard disk in the process (it might take a bit longer to boot up). Do do this, start up your computer while holding down the Shift key until the Apple logo passes. If your Mac starts up with the safe boot, go ahead and restart the computer again and see if it boots up normally (as odd as it sounds this fixes the problem a surprising amount of the time). If not, it's time to give the hard drive a closer look.

Step Three: Run Disk Utility

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If you still can't boot up OS X normally, it's time to run Disk Utility and check out your hard drive:

Boot up your computer while holding down Command+R (if you're running Snow Leopard or earlier, find your OS installation disc, put it in the drive, and reboot your computer holding down C). This will boot you into a diagnostic mode.

In a lot of cases, running Disk Utility will catch problems with startup issues. Sometimes a single file with the wrong permissions can cause the whole system to collapse, or if something's not in the right place it won't boot. If this doesn't work, you have a lot more problems to look into.

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Further Resources

If the above solutions don't work, it's time to dig a lot deeper into your system. Your problem could range from a bad hard drive to a faulty logic board. Here are a few more steps that should help you single out the problem:

The Problem: Persistent Beach Ball

Ah yes, the spinning beach ball that refuses to go away. Sometimes it's a small, application-specific problem that's easy to solve, but other times it's part of a much bigger mess. If your Mac is tossing up the spinning beach ball consistently, it's time to figure out the exact cause.

Step One: Check Activity Monitor

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Your Mac will usually get a spinning beach ball when it's somehow overloaded. More often than not, this just lasts a few seconds and goes away, in which case you can ignore it. If it doesn't, the best way to figure out what's going on is to launch Activity Monitor and pinpoint which program is causing the problem.

If you need to, force quit any programs that are potentially causing the beach ball (Command+Option+Esc).

Launch Activity Monitor (Applications > Utilities).

Now go about your daily usage. If the beach ball comes up, switch over to Activity Monitor and see which app is taking up the biggest CPU load (oftentimes this will spike at 100%).

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If it's a powerful piece of software like Photoshop that's causing problems, then it's a good chance you need more RAM in your computer. RAM can help with multi-tasking issues, and if the beach ball comes up when you're running a few programs at once additional RAM will help (this is very easy to install yourself). If not, and it's something lightweight like a file syncing service like Dropbox or an instant messenger client like Adium, then it's probably a problem with the software itself. Try quitting the app and seeing if the problem persists. If the beach ball doesn't return, then you have your problem. Check the developer's web site to see if they've issued an update, run Software Update (Apple Logo > Software Update), or get in touch with the developer if no update is available.

Another possible problem is that your hard disk is getting close to full.

Step Two: Reclaim Hard Drive Space

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When your hard disk is full it can cause spinning beach ball problems. For a lot of us, this just means cleaning up two folders: your trash and your downloads folder:

Right-click the trash can icon and select "Empty Trash." If you have a lot of stuff in there or you haven't done this recently you might get enough space to save your file.

Now head to your downloads folder (Users > Your Name > Downloads). Go through and delete any files you no longer need.

The Problem: Kernel Panics

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If you've ever experienced the black and grey kernel panic screen above, then you know how scary and completely unhelpful it is. When one application has a problem, you get the spinning beach ball mentioned in a previous section, but when multiple programs fail—or the operating system itself—you get a kernel panic. Thankfully, it's not (usually) as big of a problem as it seems.

Step One: Reboot and See If It Happens Again

In most cases, a kernel panic will force you to reboot you computer. Let this happen, and if you load right back into OS X, continue working on your computer as usual. In a lot of cases, the issue resolves itself and you can move along. If not, or if it happens only when you use specific programs, it's time to figure out what's going on.

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Step Two: Update All Your Software

Running Software Update can often fix kernel panic problems because more often than not, it's a software issue. Click the Apple icon in the top left corner, and select "Software Update." Let it look for and install new software to see if it fixes the problem.

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If for some reason the kernel panic happens when you're starting up and you can't load OS X, then you'll need to try and start up in safe mode. Reboot the computer and hold down the Shift key until the Apple logo appears. After a little while, you'll load up safe mode, a stripped down version of OS X. Here, you can still run Software Update the same way as you usually would.

It's also worth visiting the developer's web site to see if other people are having a problem with a recent update or release. If it's one specific app that always causes the kernel panic, it's best to not use it until an update is issued.

Step Three: Check Your Login Items

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If no software needs updating and you can't get your computer to start without a kernel panic then it might be an issue with one of the programs you have loading up automatically on startup. That means its time to clear out your login items. While you're still in safe mode you can remove any apps that start automatically:

Open up your System Preferences (Applications > System Preferences).

Select "Users and Groups" and select your user ID.

Select the "Login Items" tab.

Select each of the applications you have and click the minus sign to remove them from the list.

Reboot and see if you can start without a kernel panic. If so, one of those apps is causing the problem. Try loading up each to see which one causes it again.

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Further Resources

If the kernel panics keep happening and no specific app seems to cause it, you might have a bigger problem. Things start to get really tricky if you're getting kernel panics and you can't isolate the issue with any of the above methods, so here are a few guides we've found helpful for pinpointing the problem with more advanced measures.

Problem: Your Display Isn't Working or Is Distorted

This one hit me recently on an iMac. Out of nowhere, the screen turned a crazed green and yellow, and then the computer shut down. After several attempts to reboot (and trying just about everything listed above) it eventually refused to turn on. In my case, my graphics card was toast, and I had to get it replaced, but that's not always the problem. Here are a few things you can do to troubleshoot and figure out exactly why your video card or display is freaking out.

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Step One: Reset the PRAM/VRAM and SMC

This doesn't always do that much good, but it's the easiest thing to do and only takes a few seconds. Turn on your Mac and hold down Command+Option+P+R until the computer reboots. This resets the PRAM / VRAM, which is where things like startup disk selection, screen resolution, and speaker volume are stored. Sometimes this can correct display issues, and if so, continue using your Mac as you did.

The other option is to reset the SMC (System Management Controller). This controls everything on your computer ranging from the power to the fans. Every Mac has a slightly different process for doing this, so head to Apple's official SMC Reset page, find your model, and follow their instructions (this usually involves unplugging the power cord on a desktop, or removing the battery on a laptop). Once you reset the SMC a lot of your setting are restored to factory defaults and your display problems may get solved.

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Step Two: Boot Into Safe Mode

The next step to figure out what's going on with your graphics card or display is to boot into safe mode to see if the problems persist. Power on your Mac and hold down the Shift key until you get past the Apple logo. This boots into a stripped down version of OS X.

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Here, you can see if the display problems are persisting. This might be screen glitches, pixelated graphics, or large black squares everywhere. If they are, it's probably a hardware issue and you should move on to the next step. If not, it's likely a software problem, and you have a few different options for troubleshooting:

Restart the computer again in normal boot mode to see if the problem resolves itself (this does actually happen).

If not, go back into Safe Mode and check for software updates (Apple logo > Software Updates). If you get an update for your graphics card or logic board, install it.

Double-check your display options by going into System Preferences (Applications > System Preferences). Choose "Displays" and make sure the resolution and refresh rate are correct.

If you've recently installed a software update that possibly caused the issue, it's also worth checking out Apple's recently released updates and downloading and installing the most recent combo update again. Sometimes a simple re-install can fix strange issues that might have cropped up with display drivers.

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If none of those work, it's time to run the Apple Hardware test to see if it's a hardware issue.

Step Three: Run Apple Hardware Test

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A lesser known feature of Macs is the Apple Hardware Test. Like the name suggests, this is a way to test for hardware failures on your computer. It's not foolproof, but it might help you troubleshoot your issue moving forward.

Reboot your Mac and hold down the "D" key until the Apple Hardware Test starts (if you're on Snow Leopard or earlier you need to put in the install disc first).

Select your language, and then select the "Basic test" option. Let it do its thing. If an error occurs, the Apple Hardware Test should tell you which piece of hardware is failing and you've found your problem. If not, select the "Perform Extended Testing" option. This might take an hour or two to complete.

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While a hardware failure is never fun, hopefully the Apple Hardware test will actually show it so you can get the faulty hardware replaced. If it is a hardware problem, you can check out iFixit's Mac Repair Guides to see if you can fix it yourself.

Further Resources

As with any computer troubleshooting, sometimes you'll need to go through all kinds of tests and experiments to figure out what the heck is going on. If you're lucky, the above tips will get your Mac in working order in no time.